1. Field of the Invention
The present invention relates to a defect inspection method and defect inspection system for detecting a foreign matter or pattern defect in a semiconductor wafer, a photomask, a magnetic disk, a liquid crystal substrate or the like.
2. Background Art
In the process of fabricating semiconductor devices, a foreign matter or occurrence of a defect or the like in a circuit pattern results in a defective product. This is also the case with a magnetic disk and a liquid crystal substrate. Further, in the case of a photomask used to form patterns in a semiconductor wafer or a liquid crystal substrate, also, the presence of a defect causes wrong patterns to be formed in the semiconductor wafer or liquid crystal substrate, thus resulting in a defective product.
Descriptions will be given below by taking semiconductor wafer as an example. In inspecting a semiconductor wafer for defective appearance caused by a foreign matter or defective circuit pattern, the defective appearance must be quantified to check at all times the occurrence of a problem in the fabricating equipment or fabricating environment. Further, the shape of defective appearance is observed to check whether the defective appearance exerts critical effects in the product, whereby the degree of effect by the defective appearance can be determined. Instead of determining from the image of defective appearance by visual inspection whether or not the defective appearance is critical, there has recently been introduced a technique of ADC (Automatic Defect Classification) that automatically classifies the defective appearance (for example, refer to JP Patent Publication (Kokai) No. 2006-269489A).
As the defective appearance inspection apparatus, there is known an optical pattern inspection apparatus using a dark-field optical microscope (for example, refer to JP Patent Publication (Kokai) No. 05-45862A). The defect inspection mechanism which inspects a semiconductor wafer will be briefly described below. Chips constituting multiple semiconductor devices are formed on a single semiconductor wafer. These inspected chips are each typically constituted of a group of multiple patterns based on the functions of the memory area, peripheral circuit area, logic area and the like. When laser light is irradiated on the inspected object, the incident light is diffracted by the patterns, but the incident light irradiated on a defect is scattered by the defect. The diffracted light and scattered light pass through a field lens of the inspection apparatus and are adjusted to an appropriate light intensity by a variable-transmittance filter. Thereafter, the diffracted light from a pattern having a high repetitiveness such as a memory area pattern is eliminated by a spatial filter. However, the diffracted light from a pattern having a low repetitiveness such as a peripheral circuit area pattern or logic circuit area pattern, and the scattered light from a defect, which are not eliminated by the spatial filter, enters a signal detector and the signals are stored in the memory of the inspection apparatus. Then, a difference between the diffracted light signal and scattered light signal and a reference chip signal preinstalled in the memory is calculated by a difference circuit, and the difference signal is compared with a predetermined threshold level by a comparator, so that the signal greater than the threshold level is detected as a defect signal.